Nonstructural carbohydrates in dormant and afterripened wild oat caryopses

Maxine B. Nichols, Marie-Odile Bancal, Michael E, Foiey and Jeffrey J, VolenecNichols, M.B., Baneal, M.-O., Foley, ME. and Volenec, J J. 1993. Nonstructuralcarbohydrates in dormant and afterripened wijd oat caryopses. - Physiol. Plant. 88:221-228.Nonstructural carbohydrates were determined in both embryo and endosperm ofdormant (nongerminating) and afterripened (germinating) intaet caryopses of wildoat (Avenafatua L.). No ehanges in endosperm starch or soluble sugar were observedat the onset of germination (18 h). No changes in glucose, fructose, sucrose or starchwithin dormant or afterripened embryos correlated with onset of visual germination.In afterripened embryos, depletion of raffinose (18 h), stachyose (18 h) and galactose(24 h) was correlated with germination. In eontrast, raffinose-family oligosaceharidelevels in dormant embryos remained constant for 7 days following imbibition. Germi-nation of isolated dormant embryos on 88 mM galactose-eontaining media wasaccompanied by decreased endogenous levels of raffinose and stachyose. Isolatedembryos from dormant caryopses incorporated "C from '*C-fruetose into both raffi-nose and stachyose during 24 h of imbibition. In contrast, no "C incorporation intostachyose was observed in embiyos from afterripened caryopses. No '''C incorpora-tion into raffinose was observed at 18 and 24 h. When in vitro activities of a-galactosidase were measured, no temporal differences between dormant or afterrip-ened caryopses were detected in either embryo or endosperm tissue. Although themechanism associated with differences in utilization of raffinose and staehyose is yetunidentified, alterations in raffinose-family oligosaceharide metabolism in the em-bryo appear to be a unique prerequisite for afterripening-induced germination.Key words - Afterripening. Avena fatua, carbohydrate, dormancy, germination,raffinose, seed, stachyose. wild oat.M. B. Nichols, M.-O. Bancal and M. E. Foley (corresponding author), Dept ofBotany and Plant Pathology; J. J. Volenec, Dept of Agronomy, Purdue Univ., WestLafayette, IN 47907-1155, USA.I . y ing 88 mAf fructose (Fru), glucose (Glu), maltose (Mai)or sucrose (Sue), they lost dormancy (Foley 1992).Wild oat {Avena fatua L.) is one of the world's most These results suggested that a block to the utilization ofwidespread and persistent weeds (Hoim et al. 1977). these soluble sugars within D isolated embryos was notOne of its major survival characteristics is seed dor- responsible for maintenance of dormancy. This obser-mancy. The genetic variability affecting the duration of vation was of particular interest for it has been sug-primary dormancy and the afterripening requirement gested by several investigators that dormancy in wildfor germination, i.e. warm-dry conditions, are well es- oat is due to bSocks in soluble sugar utilization and/ortabhshed (Adkins et al. 1986). The physiological and accumulation (Naylor and Simpson 1961, Chen andbiochemical mechanisms responsible for transforming Varner 1969). Although exogenously applied solublethe seed from a dormant to a nondormant state are still sugars broke dormancy in D isolated embryos, theypoorly understood. were not necessary for germination in isolated after-When excised embryos from dormant (D) wild oat ripened embryos. Afterripened (AR) embryos, whenline M73 caryopses were cultured on N6 media contain- excised and cultured on N6 media, with or without